1. Field of the Invention
The present invention relates to packet relay apparatuses, and more specifically, to a packet relay apparatus that is used in a network, such as the Internet, to monitor and prevent or to monitor or prevent packet loss caused by traffic such as burst traffic.
2. Description of the Related Art
Generally, the flow of traffic exchanged among servers and terminals is not always constant and may jump instantaneously at the beginning of traffic flow (burst) or the like.
If a packet relay apparatus receives such burst traffic and if the bandwidth of the burst traffic is greater than the bandwidth of the output interface, packets are accumulated in an outgoing queue during the burst and are outputted from the queue after the burst ends, so that no packets will be lost. If the packet relay apparatus reaches its maximum relaying capability, the same step is taken in an incoming queue, so that no packets will be lost.
As the performance of servers and terminals has been improved in these days, the traffic flow of such a burst has been increasing. If the traffic flow of a burst is too large, the packets could not be accumulated in the queue of the packet relay apparatus, and some packets might be lost.
The packet loss even in an instant could degrade the reliability (UDP traffic or the like that can be affected by packet loss) or throughput (TCP traffic or the like that can be affected by packet loss) and should be avoided. It would not be appropriate, however, to lengthen the queue of the packet relay apparatus. A long queue would increase the cost of the packet relay apparatus or would retain the packets too long and overextend the delay.
To solve the packet loss problem caused by such a burst, a number of technologies for suppressing a burst by cooperation between the apparatuses or between the apparatus and the terminal have been developed. The technologies include Explicit Congestion Notification (non-patent literature 1), Backward Congestion Notification (non-patent literature 2), Priority-based Flow Control (non-patent literature 3), and Pre-Congestion Notification (non-patent literature 4). When a burst seems to cause a queue to overflow at any moment in a packet relay apparatus, those technologies give that information to the preceding packet relay apparatus or terminal to let it suppress the burst.
[non-patent literature 1] IETF, “The Addition of Explicit Congestion Notification (ECN) to IP”, RFC3168.
[non-patent literature 2] IEEE, “IEEE Standard for Local and Metropolitan Area Networks - - - Virtual Bridged Local Area Networks—Amendment: 10: Congestion Notification”, IEEE802.1Qau
[non-patent literature 3] IEEE, “IEEE Standard for Local and Metropolitan Area Networks - - - Virtual Bridged Local Area Networks—Amendment: Priority-based Flow Control”, IEEE802.1Qbb
[non-patent literature 4] IETF, “Pre-Congestion Notification (PCN) Architecture”, RFC5559